1. Field of the Invention
The present invention relates to an internal gear oil pump made of aluminum alloys (hereinafter referred to as xe2x80x9cAl alloysxe2x80x9d), the structural members thereof being less damaging to one another, exhibiting superior wear resistance, and withstanding cavitation damage in an improved manner.
2. Description of the Related Art
Generally, an internal gear oil pump typically used in the automatic transmission of an internal combustion engine mounted in a vehicle is provided with structural members such as a casing having a gear compartment, a drive gear, and a driven gear, as disclosed in Japanese Patent Unexamined Application Publication No. 8-74747. The gear compartment of the casing accommodates the drive gear and the driven gear.
It is also known in the art that the casing of the internal gear oil pump may be constituted of an Al-alloy casting, as disclosed in Japanese Patent Publication No. 7-101035. The drive gear and the driven gear are constituted of an Alxe2x80x94Si alloy powder hot plastic working material, i.e., an Alxe2x80x94Si alloy powder hot forging material and powder hot extrusion material. The above-described hot plastic working material is constituted of an Alxe2x80x94Si alloy which contains, in weight percent (hereinafter % indicates percent by weight), 12% to 42% Si and 1% to 12% transition metals such as Fe and Ni. The alloy has a structure in which ultrafine grains of intermetallic compounds and Si are dispersed in the matrix thereof. When the Si content is high, primary Si crystal grains are also dispersed in the matrix thereof.
Because internal combustion engines have recently come to accommodate higher speeds and higher outputs, the internal gear oil pumps used therein are also required to endure high-speed driving. However, the above-described conventional internal gear oil pump made of Al alloys (hereinafter referred to as xe2x80x9cAl-alloy internal gear oil pumpxe2x80x9d) has the following problems. When the Al-alloy internal gear oil pump is driven at high-speed and when the drive gear and the driven gear are constituted of an Alxe2x80x94Si alloy having a low Si content within the range of 12% to 42%, the wear resistance thereof is drastically degraded. Even when the Si content is set at an intermediate level within the range of 12% to 42%, the wear resistance is still insufficient. When the Si content is set high so that the wear resistance is enhanced, mutual damage among the structural components is increased, shortening the life of the oil pump.
Accordingly, it is an object of the present invention to provide an Al-alloy internal gear oil pump in which the structural members, particularly the drive gear and the driven gear thereof, are less mutually damaging to each other and yet exhibit superior wear resistance even when the pump is driven at high speeds. The inventors have found through extensive research and experimentation that when the conventional Al-alloy internal gear oil pump includes the drive gear and the driven gear which have the following features, the above-described object can be achieved.
(a) A hot plastic working material of Alxe2x80x94Si alloy powder which constitutes the drive gear and the driven gear is composed of an Alxe2x80x94Si alloy having a structure in which unit crystal phases are dispersed in a base matrix at 10 to 40 area percent by observation of the structure thereof using an optical microscope, the unit crystal phases being harder than the base matrix.
(b) The above-described base matrix is constituted of Alxe2x80x94Si alloy which contains 10% to 18% Si, 4% to 8% Fe, 1% to 3% Ni, 1% to 3% Cr, and the balance being Al and incidental impurities, the alloy having a structure in which ultrafine grains of intermetallic compounds and Si, preferably having an average diameter of 0.01 to 1 xcexcm, are dispersed in the base matrix.
(c) The above-described unit crystal phase is constituted of an Alxe2x80x94Si alloy which contains 25% to 40% Si, 1% to 3% Fe, 2% to 6% Ni, 0.3% to 2% Cr, and the balance being Al and incidental impurities. The alloy has a structure in which ultrafine grains of intermetallic compounds and Si, preferably having an average diameter of 0.01 to 1 xcexcm, are dispersed in the matrix of the unit crystal phase. Primary Si crystal grains preferably having an average diameter of 3 to 10 xcexcm are also dispersed in the matrix of the same.
(d) When the pump is driven at high-speed, the above-described base matrix, being soft due to relatively low Si content, is materially compatible with the base matrix of another structural member, i.e., the base matrices of the drive gear and the driven gear, and with the matrix of an Al-alloy casting. Thus, the mutual damage among the structural components can be reduced. For the engaging surfaces of the drive gear and the driven gear, an engaging surface in which high wear resistance is required, is provided with the unit crystal phases which are relatively hard due to the relatively high Si content and which serve to enhance the wear resistance therebetween. Consequently, the Al-alloy internal gear oil pump of the present invention not only has enhanced resistance to cavitation attack due to the ultrafine grains of intermetallic compounds and Si dispersed in the base matrix and the matrix of the unit crystal phase, but also displays superior functioning for a long period of time.
The present invention is based on the above-described experimental results. The Al-alloy internal gear oil pump of the present invention includes a casing having a gear compartment, a drive gear, and a driven gear, all of which are the structural components of the oil pump. The drive gear and the driven gear are disposed in the gear compartment of the casing. The Al-alloy internal gear oil pump of the present invention has the following features.
(a) The casing is constituted of an Al-alloy casting.
(b) The drive gear and the driven gear are made of an Alxe2x80x94Si alloy powder hot plastic working material, particularly a powder hot forging material and powder hot extrusion material.
(c) The hot plastic working material is constituted of an Alxe2x80x94Si alloy having a structure in which unit crystal phases are dispersed in a base matrix by 10 to 40 area percent by observation of the structure thereof using an optical microscope, the unit crystal phase being harder than the base matrix.
(d) The base matrix is constituted of an Alxe2x80x94Si alloy which contains 10% to 18% Si, 4% to 8% Fe, 1% to 3% Ni, 1% to 3% Cr, and the balance being Al and incidental impurities. The alloy has a structure in which ultrafine grains of intermetallic compounds and Si, preferably having an average diameter of 0.01 to 1 xcexcm, are dispersed in the base matrix.
(e) The unit crystal phase is constituted of an Alxe2x80x94Si alloy which contains 25% to 40% Si, 1% to 3% Fe, 2% to 6% Ni, 0.3% to 2% Cr, and the balance being Al and incidental impurities, the alloy having the structure in which ultrafine grains of intermetallic compounds and Si, preferably having an average diameter of 0.01 to 1 xcexcm, and primary Si crystal grains, preferably having an average diameter of 3 to 10 xcexcm are dispersed in the matrix of the unit crystal phase.